Proposed instrumentation systems for high voltage transmission lines include active electronic circuits which operate at transmission line potential to measure circuit parameters, for example, line current. While it is possible in some cases to provide power for these circuits directly from the high voltage ac or dc power transmission system, for example, by way of transformers or shunts, it is usually necessary to provide an alternate, independent power source to operate electronic circuits during line start-up, shutdown, or at other times when line power is not available for practical use. Power for the circuits is typically derived from a source, i.e., low voltage line power, which operates near ground potential and must be transmitted across a large potential difference to the electronics which operate at or near the potential of the high voltage transmission line.
A number of mechanisms have, in prior art, been proposed and developed to accomplish this purpose. Prior art systems have, for example, included a motor operating at ground potential which transmits power via a thin spinning rod to a generator operating at line potential and systems for transmitting power via a beam of ultrasonic energy. Generally, these prior art power transmission mechanisms operate at low efficiencies and have been characterized by poor dependability. A mechanism is, therefore, needed to efficiently and dependably power electronic instrumentation which operates at high potential with respect to ground.